Nitrogen loss due to ammonia volatilization occurs with urea or urea-based fertilizers, in part, because of rapid hydrolysis of urea on or near the soil surface by microbially generated urease enzymes. A urease inhibitor such as a phosphoric triamide or thiophosphoric triamide (particularly N-(n-butyl) thiophosphoric triamide, NBPT) can slow down the enzymatic breakdown of urea by inhibition of the urease enzyme. This provides an effective means of managing losses of nitrogen in the form of ammonia from surface-applied urea containing fertilizers.
A phosphoric triamide or thiophosphoric triamide such as NBPT as a urease inhibitor can be applied onto a granular fertilizer formulation by first blending a concentrated solution of the phosphoric triamide or thiophosphoric triamide that is dissolved in a solvent such as a glycol or glycol derivative or a mixed solvent of a glycol or glycol derivative and a liquid amide (See U.S. Pat. No. 5,698,003). Alternatively, a phosphoric triamide or thiophosphoric triamide urease inhibitor such as NBPT can be introduced into a urea melt to form an incorporated urea fertilizer (See WO 2015/027244). In addition, a highly concentrated dry formulation of NBPT such as AGROTAIN® DRI-MAXX nitrogen stabilizer, which can adhere to the urea granules without adding additional moisture to the blend, can be used to treat urea granules to make a NBPT-containing urea as well (See U.S. Pat. No. 9,034,072).
Industrial grade N-(n-butyl)thiophosphoric triamide (NBPT) is a waxy-like solid compound, which is not easy to use directly and which is also sensitive to moisture and elevated temperature. The use of a liquid formulation of NBPT is thus highly desirable because it greatly facilitates the introduction of the NBPT onto granular urea and into liquid fertilizers containing urea. Suitable solvents to prepare NBPT solutions should comply with some basic requirements such as high solubility and stability of NBPT in the solvent, resistance of the resulting NBPT solutions against crystallization or freezing at a low temperature, low viscosity of the concentrated solutions of NBPT, low toxicity, volatility and flammability, minimum content of water in the commercially available form of the solvent, and low cost.